Minimization of sheet thickness variation and other defects of mini drawn parts using a blank holder plate made from concentric rings

Thickness variation is a major defect of the drawn parts made from sheet metals, which influences the intensity of part defects and may cause part failure. In the case of mini deep drawing, sheet thickness variation along part's profile has the following effects on the drawn part geometry: increased non-uniformity of diameter variation, variation of springback parameters (part edge radius deviations and angle of wall inclination), different wrinkling intensities, and part cracking and fracture. The present paper analyses the experimental results of the investigations concerning the sheet thickness variation in the case of mini cylindrical drawn parts made from a copper alloy. Some constructive solutions of tool components that allow the control and minimization of sheet thickness variation by controlling the blank holder force, contact and friction forces (especially in the part flange zone) are also proposed and tested by simulation and experiment. The constructive solutions of the new tools were obtained by constructing the blank holder plate from two concentric rings made from different materials with equal or unequal widths.     

镀层薄板拉深过程中镀层厚度变化影响因素分析

对镀层板料拉深成圆筒件的过程进行模拟及试验研究,得到了圆筒件各部分镀层厚度的变化规律。选取镀层最薄处厚度为镀层质量评价因素,利用LS-DYNA软件,基于正交法分析了拉深过程中的主要工艺参数（压边力、凹模圆角半径、凸模入口圆角半径和摩擦因数）对镀层厚度变化的影响规律,并结合拉深机理对其进行了深入研究,得到了所选工艺参数的最优组合。     

电沉积纳米镍薄板的超塑微拉深性能

采用脉冲电沉积工艺制备了厚度为0．1mm的纳米镍薄板，在不同的温度和应变速率下对该薄板进行单向拉伸试验，确定了其超塑性变形的最佳工艺条件，在此基础上进行了纳米镍薄板的微拉深性能实验。实验结果表明：纳米镍薄板的微拉深性能随成形温度的升高而提高；在温度为723K、半球形拉深凸模直径为1mm、拉深速度为1～5mm／min的条件下，均可成功拉深出半球件。采用透射电镜和扫描电镜对拉深变形前的沉积态组织和拉深变形后的微观组织进行了观察比较，结果表明，微拉深后大部分镍晶粒长大到微米量级。根据实验结果，初步探讨了超塑微拉深的主要变形机制。     

Investigation of hydrodynamic deep drawing for conical�Ccylindrical cups

Forming conical parts is one of the complex and difficult fields in sheet-metal forming processes. Because of low-contact area of the sheet with punch tip in the initial stages of forming, bursting occurs on the sheet. Moreover, since most of the sheet surface in the area between the punch tip and blank holder is free, wrinkles appear on the wall of the drawing part. Thus, these parts are normally formed in industry by spinning, explosive forming, or multi-stage deep drawing processes. In this paper, forming pure copper and St14 conical?Ccylindrical cups in the hydrodynamic deep drawing process was studied using finite element (FE) simulation and experiment. The effect of pressure path on the occurrence of defects and thickness distribution and drawing ratio of the sheet was studied. It was concluded that at low pressures, bursting occurs on the contact area of sheet with punch tip. At higher pressures, the cup was formed, but the wall thickness distribution depends on the pressure path. It was also illustrated that for the pressure path with a certain maximum amount, the workpiece was formed adequately with minimum sheet thickness reduction. Internal pressures more than this maximum amounts did not affect on the thickness distribution. By applying the desired pressure path, conical?Ccylindrical cups with high deep drawing ratio were achieved.     

数值模拟的双层金属板拉深成形工艺研究

某轿车排气歧管保护罩采用双层镀铝钢板同步拉深工艺制成,为获得最佳成形工艺参数,避免拉深时产生严重减薄及起皱现象,采用Dynaform软件对双层金属板同步拉深成形过程进行了有限元数值模拟,分析了压边力对拉深成形过程的影响,获得了不同压边力下保护罩内、外层板的壁厚减薄与增厚分布规律。结果表明,与单层板拉深成形相似,对于复杂型面双层金属板拉深件而言,单纯增加压边力并不能完全避免拉深过程中的起皱现象;采用压边力及合理布置拉深筋,可以保证内、外层板材料塑性流动均匀,有效抑制起皱、拉裂等缺陷。根据数值模拟结果进行了产品试制,获得了质量合格的拉深件。     

Indexing and retrieval in case-based process planning for multi-stage non-axisymmetric deep drawing

This paper presents a case-based reasoning (CBR) methodology for computer-aided process planning (CAPP) for multi-stage, non-axisymmetric sheet metal deep drawing. The methodology addresses the indexing and retrieval of process planning cases. Planning cases are indexed via a feature-based representation of deep drawn parts. Efficient case retrieval is achieved by a feature-based similarity analysis between a new deep drawn part and existing parts in the case library. An illustrative example is included to demonstrate the operation of the proposed approach and show its effectiveness in speeding up CAPP for multi-stage non-axisymmetric deep drawing. This revised version was published online in April 2005 with a correction to the corresponding author’s address.     

Deep drawing of rectangle parts using variable blank holder force

When deep drawing rectangle parts, instead of adopting elastic or several segmented blank holders, a new thought of applying dual layers of blank holders, which are parallel to each other, has been achieved to asynchronously vary blank holder force (BHF) at different regions of sheet flange, by dint of replacing different little mandrils in length between dual layers of blank holders, thus to further improve the formability of products. At the same time, in order to solve two problems of how to judge which one distribution of one desired integral variable BHF, which was obtained from the thickness analyses with products in advance, on blank holder for asymmetric parts is the best and to evaluate lubricant in deep drawing, a probe sensor with structure of dual cantalevers, based on the theory of resistance strain slice, fixed into the inner space of die, was developed for measuring real-time friction coefficient of sheet flange’s surface. Through this special probe sensor, not only real-time BHF on sheet flange could be measured out, but also the real-time friction coefficient could be figured out. Finally, one example of rectangle part was carried out in tests to validate the feasibility of this thought. By the way of analyzing the distribution of variation with products’ thickness on products and judging whether the whole distribution of friction on sheet flange’s surface was uniform or not, one optimized BHF loading profile could be finally obtained over the whole punch stroke.     

圆筒件拉深变形过程中应力分布的数值模拟

拉深是拉深类零件的一个基本成型工序,为考察冲压拉深变形过程中材料的应力分布状态,利用ANSYS有限元软件对紫铜板拉深过程进行数值模拟。结果表明,拉深变形过程中变形主要集中在处于凹模端面上的凸缘部分,凹模圆角部变形比较复杂,易发生应力集中现象而导致材料被拉断,合理的压边可有效防止拉深起皱。     

圆锥形件拉深成形应力应变的直接积分解法

针对圆锥形件的拉深成形,在平面应力和比例加载条件下,采用参数方程的方法分析得到了变形区应变的微分方程。可在圆锥形件的凸缘区、凹模圆角区及锥壁区分别根据应变微分方程,代入相应的边界条件,采用直接积分得到应力、应变解,将应用于轴对称平面内的积分解法推广至分析圆锥形件的拉深成形问题。在凸缘区,锥角等于0;在锥壁区,锥角等于一定值;在凹模圆角区,将圆角部分的弧段分成若干个微锥段,每一微锥段都可分别作为一个小的等锥角的锥环处理。采用该方法,不仅可以计算锥形件的拉深成形问题,而且可以计算曲面形状已知的一般轴对称曲面零件的成形问题。用直接积分法替代迭代法求解非线性方程,使求解过程大大简化。 选取厚0.87mm 的ST16板材进行了拉深成形实验,以板坯内层为测量面,测量了凸缘区、凹模圆角区和锥壁区的应变分布,理论计算结果与实验结果一致。     

AZ31镁合金盒形件变压边力温热拉延工艺

通过温热交叉轧制工艺制备了板形以及成形性能良好的AZ31镁合金薄板;开发了可加热的变压边力双动液压机,并详述其工作原理;采用不同的压边力方案,对盒形件进行温热拉延实验,分析了变压边力对AZ31镁合金板材温热拉延性能的影响。结果表明:最佳的压边力变化方案是压边力随凸模行程先增后减的模式;采用变压边力技术可以将AZ31镁合金盒形件的拉深深度提高13·2%。     

采用可移动凹模的板材液压成形技术

提出一种改进的板材液压成形新工艺,即采用可移动凹模,实现拉深与胀形的复合液压成形。在整个变形过程中,板材初始变形部分始终与可移动凹模接触,从而抑制已变形区进一步变形,使变形更加均匀,实现变形的顺序控制,板材成形极限得到提高。从试验和数值模拟两方面对可移动凹模板材液压成形技术进行了研究,分析各种工艺参数,如摩擦因数等对板材成形性的影响,并且分析了可移动凹模对板材成形极限的影响。     

The effect of nanoparticulate loading on the fabrication and characterization of multi-doped Zn-Al2O3-Cr2O3 hybrid coatings on mild steel

In this paper, an improved approach is proposed to determine the optimal profiles of two controllable process parameters (hydraulic pressure and blank holder force), which improve the forming condition and/or make better use of forming limits in hydromechanical deep drawing (HMD) process. A method based on adaptive finite element analysis coupled with fuzzy control algorithm (aFEA-FCA) was developed using LS-DYNA to determine the optimal loading profiles and thus to maximize the limiting drawing ratio (LDR). Maximum thickness reduction, maximum wrinkle height in the flange region of the sheet metal blank, and position of the nodes in the unsupported portion of the sheet metal blank between punch and die were used as criteria in the fuzzy control algorithm. Different rule-based matrices were compared by considering the maximum thinning occurred in the sheet metal blank, and thus, the most accurate matrices were determined for the control algorithm. The optimal loading profiles could be determined in a single FEA, thus reducing the computation time. The proposed approach enables determining the optimal loading profiles and also could be applied to complex parts easily. In addition, effects of initial blank diameter and coefficient of friction between the sheet-blank holder and sheet-die on the optimal loading profiles were investigated. An attainable LDR of 2.75 for AA 5754-O sheet material in hydromechanical deep drawing process was proven experimentally using the optimal loading profiles determined by adaptive FEA.     

圆筒件拉深过程中压边力的研究

利用恒定压边力经验公式计算得到的压边力值进行模拟时,圆筒件质量存在明显的缺陷。采用变压边力优化曲线作为圆筒件拉深成形的压边力加载模式,研究了临界防皱变压边力曲线的确定方法,应用Dynaform软件对恒定压边力、优化压边力下圆筒件的拉深成形进行了数值模拟,得出了成形极限图(FLD)和材料厚度变化图。将模拟结果进行对比分析,发现在后者作用下的圆筒件平面外缘厚度变化较小,筒壁等其他部分的材料厚度变化率也较小,采用优化压边力可有效防止圆筒件起皱、拉裂现象,提高圆筒件成形质量。     

球形件反复拉深成形工艺有限元模拟及试验

提出了球形件反复拉深成形工艺,对该工艺进行了有限元模拟与试验验证。与一次拉深成形工艺进行了对比分析,结果表明：凹模圆角区与法兰区应力状态及大小基本相同,但在球底区,反复拉深时径向应力和周向应力都远小于一次拉深的应力,球底区径向应力和周向应力基本为压应力或很小的拉应力;反复拉深时球底区厚度方向应变明显减小,一次拉深、二次反复拉深、三次反复拉深成形的制品最薄点减薄率分别为0.189、0.122、0.049,三次反复拉深可实现近等壁厚制品的拉深成形。该工艺与筒底冷校形工艺相结合,可实现近等壁厚深筒形零件的拉深成形。     

A hybrid NN-FE approach to adjust blank holder gap over punch stroke in deep drawing process

In deep drawing process, the blank holder plays a key role in adjustment of metal flow into the die cavity. Moreover, the quality of drawn parts is extremely affected by this flow. There are two methods of treating the blank holder in deep drawing and its simulation. One is blank holder force (BHF) and the other is blank holder gap (BHG), defined as the fixed distance between the blank holder and the die surface. In previous studies, a large number of experimental techniques have been used to study BHF; however, the amount of theoretical and numerical simulation work to study BHG is insufficient. In the present study, the concept of BHG profile, i.e., variation of BHG over punch stroke is introduced and it is shown that a properly selected BHG profile can improve the section thickness of formed part and result in the drawing of deeper parts. Here, two methods for the optimization of BHG profile are devised, i.e., the local optimization and the global optimization methods. In the first approach, the best BHG in each punch step is determined and finally, the local optimized BHG profile is achieved. In the second method, however, the empirical model for the prediction of final minimum section thickness in terms of BHG profile is obtained using design of experiments and neural networks. In the next stage, the proposed model is implanted into a simulated annealing optimization procedure to identify a proper BHG profile that can produce the desired blank thickness. Afterward, the BHG profile approach is applied to a variety of initial thicknesses, blank diameters, and materials in order to examine the robustness of method. In this paper, ABAQUS finite element package is used to gather finite element (FE) data and several experiments are performed to verify the FE results.     

薄壁深抛物线形零件固体颗粒介质成形工艺

薄壁抛物线形壳体成形过程为拉深和胀形两种变形模式的复合,极易发生起皱和破裂。固体颗粒介质成形是采用固体颗粒代替刚性凸模或凹模(或弹性体、液体)对板料进行成形的工艺。板材在颗粒介质内压的作用下成形,可以有效防止抛物线形件拉深成形过程中侧壁的起皱;由于颗粒内压是非均匀分布的,故可以有效控制抛物线形件成形过程中的破裂,提高板材的成形极限。根据固体颗粒介质成形工艺的特点,提出了两次成形薄壁深壳体零件的工艺,建立了数值分析模型,通过数值模拟和试验对该成形过程和工艺参数进行了分析。结果表明,采用固体颗粒介质成形工艺过程简单、成形工件壁厚分布均匀、表面质量好、回弹小。     

点阵热源加热板料成形技术研究

初步试验验证板料温成形中,采用离散化热源和均匀热源相比能够进一步提高板料成形性能的基础上,提出点阵热源加热板料温成形新技术。基于有限元仿真,采用0Cr18Ni9不锈钢板料对点阵热源加热成形过程进行验证和初步研究。研究结果表明,点阵热源加热板料成形工艺是完全可行的,在相同热量的情况下,通过控制点阵热源的分布可以得到比均匀热流加热更大的极限拉深比;采用点阵热源加热拉深得到的零件壁厚分布一般存在两个明显的谷值,第一个谷值点在凸模圆角处,和最大拉深力有关,第二个谷值点在零件直壁上,是由于凸缘部位的高温材料拉深成直壁变成传力区以后因温度高承载能力下降引起的。     

不同硬化模型对铝合金板冲压成形模拟结果的影响

研究不同塑性变形硬化模型对汽车5182-O铝合金板材冲压成形模拟结果的影响。采用材料单向拉伸试验得到应力应变关系曲线,基于Hollomom、Krupskowsky与Power方程对曲线进行拟合,建立材料室温下塑性变形硬化模型,对厚度为1.5 mm和0.85 mm的5182板材进行冲压试验和有限元模拟分析,对比分析冲压试验与模拟结果。试验与模拟结果显示,当板料厚度为1.5 mm时,板料冲压试验的成形力最大为42.95 kN,板料拉深深度为30.58 mm,基于Power方程计算得到的最大成形力为41.5kN与试验结果比较接近,Hollomom方程计算得到的拉深深度为30.546 mm,板材成形厚度分布与试验结果比较接近;当板料厚度为0.85 mm时,板料冲压试验的成形力最大为34.47kN,板料拉深深度为33.792 mm,基于Power方程计算得到的最大成形力为34.27 kN与试验结果比较接近,Hollomom方程计算得到的拉深深度为33.636 mm,板材成形厚度分布与试验结果比较接近。基于三种硬化模型铝合金冲压成形过程的计算模拟分析结果,并通过与试验对比得到不同硬化模型对铝合金板材冲压成形计算模拟的影响,进一步为汽车铝合金覆盖件在成形工艺的研究分析提供理论指导。     

盒形件固体颗粒介质板材成形工艺研究

固体颗粒介质板材成形工艺是采用固体颗粒微珠代替刚性凸(凹)模(或弹性体、液体)的作用对板材拉深成形的新工艺。选用非金属固体颗粒介质——GM颗粒作为研究对象,以固体颗粒介质在高应力水平下的体积压缩试验和摩擦强度试验为基础,应用散体力学理论中扩展的Drucker-Prager线性模型构建固体颗粒介质有限元材料模型。以具有非轴对称性的方盒形件为代表,进行固体颗粒介质成形工艺的有限元模拟,研究成形过程中板材的流动特征和壁厚分布规律。工艺试验成功得到方盒形零件,将加载曲线、成形过程变形特征和壁厚分布曲线与数值模拟结果比对较为吻合。分析表明,采用以散体力学为基础建立的固体颗粒介质材料模型进行工艺模拟,能够得到与试验较为接近的变形特征和力能参数,可以应用于制定工艺方案的依据,为该技术在板材成形中的应用起到指导和借鉴作用。     

Redrawing analysis of aluminum–stainless-steel laminated sheet using FEM simulations and experiments

The behavior of two-layer aluminum–stainless-steel (AL-SUS) laminated sheets during deep drawing, direct and reverse redrawing processes (first and second drawing stages), have been examined by simulations and laboratory experiments. For the simulation a rigid-plastic finite element program has been used. The results of simulations are presented as the variation of drawing ratios with respect to various thickness ratios and setting conditions. They show that to achieve the highest drawing ratios in direct and reverse redrawing, the thickness ratio should be about (one-layer aluminum and three-layer stainless-steel) and the setting conditions are opposite to each other. Considering the FEM results, laminated sheets with a thickness ratio of 71.3% aluminum and 28.7% stainless-steel were used to prepare deep drawing and redrawing experiments. The results of experiments are presented as the variation of thickness strain distribution in the drawn cup and punch load–stroke curves with respect to the setting condition. Results show that while in direct redrawing, contact of stainless-steel with the punch leads to the maximum drawing ratio, in reverse redrawing, aluminum should contact the punch in order to achieve the highest drawing ratio. An explanation for this finding is offered based on the thickness strain distribution, and punch load–stroke curves.